Generally, a steering system is used that assists in separate power, as a system for assuring a steering safety of a vehicle. A conventional auxiliary steering system used to employ hydraulic pressure, but recently an electronic power steering system (EPS) excellent in accuracy and having less power loss is used.
The EPS is adapted to transmit a rotation output of an electric motor to a steering shaft via a speed reduction mechanism. In other words, the EPS is operated in such a manner that a motor is driven by an electronic control unit based on travel conditions detected by a vehicle speed sensor, a torque angle sensor and a torque sensor to thereby insure a rotational stability and to provide a quick restoring force, whereby a driver can drive a vehicle safely.
The EPS is such that a torque manipulating a steering wheel for steering by a driver is assisted by a motor to allow a steering operation with less power, where a BLDC (Brushless Direct Current) motor is usually used for the motor. The BLDC motor is a DC motor mounted with an electronic rectifying mechanism except for mechanical contact areas such as a brush and a rectifier.
FIG. 1 is a lateral cross-sectional view illustrating a motor according to prior art.
Referring to FIG. 1, the conventional motor includes a substantially cylindrical upper-opened housing (1) and a bracket (2) coupled to the upper surface of the housing (1).
The housing (1) and the bracket (2) are respectively supported by a rotation shaft (3). The rotation shaft (3) is connected thereon with a steering shaft of a vehicle to provide an assisting power to steering as mentioned above. A periphery of the rotation shaft (3) is formed with a rotor (5) comprised of a core and a magnet, and the housing (1) is coupled at an inner surface thereof with a stator (4) formed with a core and a coil to provide an electromagnetic force to the periphery of the rotor (5).
In a case a current is applied to the stator, the rotor (5) is rotated by an electrical mutual action between the rotor and the stator, whereby the rotation shaft (3) is rotated to assist the rotation of a steering shaft.
The bracket (2) is mounted thereon with a PCB (8, Printed Circuit Board) formed with a sensor (9), and a plate (6) is coupled thereto to rotate with the rotation shaft (3) discrete at a predetermined space on an upper side of the PCB. The plate (6) is arranged thereunder with a sensing magnet (7). The sensing magnet (7) is rotated along with the rotation of the rotation shaft (3) to calculate a rotation angle based on changes in magnetic flux based on rotation detected by the sensor (9).
Thus, the steering torque can be assisted by rotating the rotation shaft through application by the motor of an appropriate current to the stator based on the rotation angle.
Meantime, the coupling between the plate (6) and the sensing magnet (7) is made by an adhesive, such that there may arise a problem in adhesion process between the plate (6) and the sensing magnet (7) to create a possibility of disengaging the magnet. Particularly, the adhesion problem may worsen where the coupled relation has to be maintained by a coupling power of the adhesion alone in light of variably changing environmental condition of a vehicle.
The conventional structure may pose problems involving economic matters of selecting and using a high-priced adhesive and requiring a more accurate adhering process than that of an adhesive coating process.